Dual purpose tanks for providing both fuel storage and water ballast are presently available for use on marine vessels. Such a tank encloses a plurality of internal compartments formed between spaced internal walls having openings formed therein through which flow of the fuel and ballast water is conducted along interfaced flow paths between two flow ports respectively located adjacent opposite side walls of the tank.
The foregoing type of tank is utilized because it conserves a significant amount of hull volume otherwise assigned to separate tanks for different functions such as storage of fuel, refueling and water ballast on ships. A major disadvantage of such multi-purpose tanks involves mixing of the fuel with water during the refueling operation resulting in overboard discharge of fuel with the water thereby creating an environmental pollution problem. Also a large amount of water is retained so as to further limit fuel capacity. Such large amount of water retention occurs in current tank configurations during refueling when the fuel/water interface reaches a critical level in a predetermined compartment internally of the tank within which there is uneven fuel distribution. It is therefore an important object of the present invention to provide marine vessels with the foregoing type of multi-purpose tank internally structured to reduce fuel and water mixing so as to minimize overboard discharge of fuel in compliance with present and future environmental pollution regulations and increase useable fuel capacity.